Prior to describing pressure sensors, the general characteristics of magnets used herein will be explained first.
Magnets are made of a material having a magnetic force for attracting iron powder. A strong, industrially fabricated magnet is referred to as a permanent magnet, and is also referred to in brief simply as a magnet.
Iron powder placed beside the magnet is attracted to the magnet. The space under the influence of this magnetic force is referred to as a magnetic field. In other words, the magnet can be understood to produce the magnetic field. The shape of the magnetic field can be displayed using a pattern of iron powder. When iron powder is uniformly scattered on a thick sheet of white paper placed on the magnet, the lines of magnetic force are observed in a specific pattern. The needle of a small compass placed along one of the lines of magnetic force is oriented according to the direction of the line of magnetic force from the N pole to the S pole.
The magnitude of the force between the two poles is determined according to Coulomb's law, that is, it is inversely proportional to the square of the distance between the poles but proportional to the strength of the magnetic poles. Since the magnetic poles are composed of a pair of N and S poles having the same strength, the magnetic moment is considered a more essential physical quantity than the strength of the magnetic poles. The magnetic moment is expressed as a vector directed from the S pole towards the N pole. The force calculated between two magnetic moments is proportional to the fourth power of the distance. Thus, the attractive force between two magnets is strong when the magnets are placed near each other, but quickly drops when the magnets are separated from each other.
Magnetization occurs when magnetic zones change properties of a structure, such as the shape, arrangement and orientation thereof. Once magnetized, the changed structure rarely changes its state or returns to its original state, owing to residual magnetization, even after a magnetic field has been completely removed. A material having residual magnetization to a great extent is referred to as a permanent magnet.
Magnetic flux is produced by integrating magnetic flux density or magnetic induction for a sectional area perpendicular to the direction thereof. The magnetic flux is expressed in maxwells (with the symbol Mx) in the CGS system or in webers (with the symbol Wb) in the MKS or SI system. As the magnetic flux passing through a coil changes according to time, voltage proportional to the rate of change is present at both ends of the coil (i.e., Electromagnetic induction of Faraday). This voltage is induced in the direction in which a magnetic field created by current interrupts any change in magnetic flux. This is called Lenz's Law. The magnetic flux is created by a permanent magnet or a current flowing through a coil.
Various types of sensors may be used according to methods for detecting a magnetic field. A Hall sensor is probably the best-known sensor. The Hall sensor is operated by an electric current applied to electrodes of a semiconductor device (Hall device). After the electric current is applied to the electrodes, a magnetic field is induced vertically to cause an electric potential in a direction perpendicular to both the current and the magnetic field.
The Hall sensor is the simplest distance-measuring device, using a permanent magnet and a detector for magnetic flux. The Hall sensor measures changes in magnetic flux density according to distance from the permanent magnet, and thus determines the distance based on the electric potential caused by the detector.
However, since the magnetic flux density generated by the permanent magnet is not linear according to distance, the Hall sensor should be equipped with a program or an electronic circuit for compensating for non-linearity in order to function as a more accurate distance-measuring device. In addition, many studies have been carried out to provide a structure capable of measuring linear magnetic flux density in order to compensate for the non-linear distribution of magnetic flux density according to distance. Such structures include several types of magnets and combinations thereof.
Recently, many types of non-contact distance-measuring devices have been developed in order to detect the absolute position of a body while measuring linear and angular displacement.
There are various types of non-contact distance-measuring devices. A device using a sliding register potentiometer is best known, but is not sufficiently reliable. An optical positioner is an optical sensor for reading optical ranges such as slits, but has a complicated structure. There is an approach of using a magnetic sensor to read magnetic sections on a magnetic medium, but this has a complicated structure and absolute position cannot be detected.
That is, only the distance between two points can be measured. The present invention aims to utilize a magnet having linear magnetic flux density, capable of detecting the absolute position of a body to be measured. By using the magnet having a very simple structure, a long measuring range and a high reliability, it is possible to measure distances more accurately using an inexpensive sensor without having to use a program or electronic circuit for compensating for non-linearity.
The present invention involves a pipe connecting negative and positive pressures, a diaphragm movable in response to the difference between negative and positive pressures, a diaphragm support attached to one side of the diaphragm, a magnet attached to the diaphragm support to radiate linear magnetic flux density, a spring supporting the magnet and the diaphragm, and upper and lower cases housing these components.
The term “pressure” indicates force acting on contact surfaces of two objects, in which the two objects contact and push each other in a direction perpendicular to the contact surfaces. The pressure may also be force acting inside a single object when internal parts push each other. In this case, both parts are considered to apply the force (stress) against each other on a single face inside the object. If the force is not perpendicular to the face, the force is divided into a component that is perpendicular to the face and another component that is parallel to the face, in which the force component that is perpendicular to the face is also referred to as pressure (pulling force is referred to as ‘tension’).
Since pressure uniformly acts on a face, the intensity of pressure applied to every point on the face is determined differently according to the area of the face even with the same total force (total pressure). When a force or pressure having a magnitude of P is applied uniformly on an object having a size of S, the intensity of pressure is defined by P/S. When an object is placed on a table, the intensity of pressure is generally different according to the position of a contact face. The intensity of pressure on each point of the contact face can be obtained from a minute area including the point. The intensity of pressure is also referred to simply as ‘pressure’.
Several types of pressure sensors are currently used, and are selected according to the object to be measured.
The objects to be measured may be classified generally into fluids, solids and gases. A stress gauge is a representative pressure sensor for measuring the pressure of solid objects. However, a diaphragm is generally used to measure the pressure of fluid or gas, since the relative pressure of fluid or gas has to be measured.
The relative pressure can be measured based on the displacement of the diaphragm in combination with a spring, in which the diaphragm is displaced by a relative pressure difference.
The present invention relates to a sensor for measuring relative pressure using a diaphragm and a spring, which can be used variously to measure the pressure of fluid or gas.
The present invention provides an embodiment that is applicable to a boiler having a pressure sensor capable of measuring the flow rate of inflow air. Conventionally, an on/off type pressure sensor (wind pressure sensor) has been used to measure the air pressure (wind pressure) in a boiler. In the pressure sensor (wind pressure sensor), the pressure of air introduced by an air blower is transferred to the diaphragm of the sensor so that a micro-switch attached to the diaphragm switches on/off an electric circuit to regulate the rate of flow of air. However, since the pressure sensor is used at a fixed operating pressure, the pressure sensor is determined according to the type of the air blower.
In addition, the pressure sensor does not accurately measure the flow rate of inflow air. The pressure sensor can merely assist in increasing/decreasing the pressure (flow rate) of inflow air by regulating the rotating speed of the air blower according to the pressure of inflow air.
Various types of pressure sensors are used to detect the pressure of fluid, and several types of pressure sensors capable of detecting flow rate using flow pressure (differential pressure) have been proposed.
FIG. 1 shows a conventional pressure sensor for sensing water level, as disclosed in Korean Utility Registration No. 0119708. As shown in FIG. 1, the pressure sensor includes a body 100 having upper and lower covers 110 and 130 and a diaphragm 140 arranged inside the body 100. The pressure sensor detects the pressure in a hydraulic chamber 131 based on a change in the diaphragm 140, which is caused by a pressure change in the hydraulic chamber 131. The pressure sensor also has a light shielding member 200 configured to change its cross section in proportion to the change in the diaphragm 140 in order to control the amount of light passing through the light shielding member 200. A light emitting device, such as a Light Emitting Diode (210), and a phototransistor 220 are arranged on opposite sides of an elevating path of the light shielding member 200 relative to each other. A tubular body 150 having threads 151 in the inside wall is arranged in the upper cover 110, and a spring 160 having a predetermined elasticity is contained in the tubular body 150. The elasticity of the spring 160 is adjustable according to the upward/downward movement of a cover 170, which is screwed into the threads 151 in the inside wall of the tubular body 150. With this arrangement, the pressure in the hydraulic chamber 132 is detected based on the output voltage of the phototransistor 220, which is variable according to the quantity of light applied from the LED 210. Consequently, the pressure sensor can detect the water level based on a change in voltage, which is determined by a change in the quantity of light from an optical coupling device.
FIG. 2 shows another type of pressure sensor, disclosed in Korean Utility Registration No. 0273056. As shown in FIG. 2, the pressure sensor includes a housing member 10 which has a space 13 for fluid received and discharged through circulation ports 11a and 12a and a diaphragm 14 flexing upward and downward due to the elasticity of an elastic body in response to the pressure of fluid. The pressure sensor also has a permanent magnet 20 for moving upward and downward in an operating region in response to the diaphragm 14 and a sensor member 30 arranged adjacent to the operating region of the permanent magnet 20 to detect the magnetic force thereof. Using the sensor member 30, the pressure sensor can detect a change in the magnetic force of the permanent magnet 20, which moves precisely in response to changes in the pressure of the fluid, thereby more accurately measuring changes in the flow rate and/or the pressure of fluid.